Objectives
In the original VVER-440/230 design, two safety relief valves were provided for each steam generator on the secondary side. These valves were not qualified to relieve water and their operability was not proven to be reliable. The IAEA Issue Book for VVER 440/230 reactor types identified this issues (S12) in Category II.
Consequently the European Commission launched a project to address this issue in the framework of TACIS 96' nuclear safety programme.
The overall objective of this project was to procure and install the new steam generator safety valves and associated I&C interface.
Background
The Armenian Nuclear Power Plant (ANPP) consists of two units of the VVER/440/270 model Soviet type reactor that is a modified version of the VVER/440/230 in view of special seismic design considerations. Unit 1 started its commercial operation in 1976 and Unit 2 in 1980. Both units were shut down shortly after the 1988 Spitak earthquake. Re-commissioning works were performed from 1993 to 1995 and in November 1995 Unit 2 restarted operation.
The original configuration of steam generator safety valves (SGSV) comprised the two valves, each 50% capacity. SGSV were not qualified for the two-phase flow; they were partially qualified for seismic loads.
Project Results
The replacement of steam generator safety valves involved the following activities (performed by the EC Consultant):

• Analysis of safety functions to be performed by the new valves,
• Preparation of procurement technical specifications,
• Assistance for SGSV testing, installation and commissioning, and
• Support to ANPP in licensing related activities.

The Supplier BOPP & REUTHER was selected in the EC tender procedure, and respective supply contract was placed in April 1999. The supplier delivered SGSV on site in November 1999. Due to lack of financial resources at ANPP side, the installation of SGSV was postponed to the next outage in 2000.
NIAEP, the Russian architect designer of ANPP steam conversion system performed associated T/H analysis and elaborated corresponding design files, i.e. installation design of BOPP & REUTHER SGSV and associated piping at ANPP main steam lines, including I&C interface. The installation activities were performed by the ANPP staff under the supervision of the supplier.
The licensing related activities were performed on the 2+2 basis; the European Consortium Riskaudit worked together with Armenian nuclear safety authority (ANRA) to review SGSV design files and amendments to the plant technical safety justification report.
The new SGSV were installed at ANPP Unit 2 during the plant outage in 2000. The SGSV commissioning tests were successfully performed. The plant design and operating documentation (operating limits and conditions, operating manual, safety justification) was updated to reflect the SGSV settings, operating and testing requirements. The plant restarted again in December 2000.